Python 3 readline 'bug'

gistfile1.py

# cat readline.py
f = open('test.txt', 'r')
print(f.readline())

import subprocess
p = subprocess.Popen(["cat", "test.txt"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)

print(p.stdout.readline())
# python3 readline.py
bla

b'bla\n'